Microsoft Corp. created the world's most popular operating system — one that's also heartily embraced by hackers and virus writers. And it begat the world's top Web browser, which makes it all too easy to mistakenly download and install spyware, adware and other garbage.

You'd think the world's largest software company, which presumably knows its own Windows and Internet Explorer code, would have long ago come up with something to repair PCs possessed by malicious programs.

Think again.

Though Microsoft regularly releases bug fixes, security patches and even the occasional virus-removal tool, it has only recently made programs available to help people wrangle back control of their computers after they've clicked the wrong pop-up ad, opened a rogue attachment or installed adware-packed freebies.

The company now has two free programs to help rid PCs of unwanted pests. Though Microsoft Windows Malicious Software Removal Tool and Microsoft AntiSpyware show some promise, they aren't close to being magic bullets.

I tested the programs on a Windows XP computer I borrowed from my wife's cousin. The 3-year-old PC, a Gateway running Windows XP Home Edition, was basically unusable.

Annoying pop-up windows, a sign of adware, were the least of its problems. The modem dialed phone numbers even though the PC was hooked up to a broadband connection. It took more than a minute to load a single Web page and often crashed minutes later.

Error messages appeared when I tried to open the Task Manager, a Windows utility that shows running programs and processes. It refused to load Windows Update, Microsoft's site for downloading security patches and other fixes.

Needless to say, the machine had not received any security updates from Microsoft in a while. To load Microsoft's Malicious Software Removal Tool, I had to get it using another machine, load it on a USB drive and install it manually. (It's usually available through Windows Update.)

Once installed, the tool scanned the machine and reported no problems, even though there were big problems.